Self-regulation skills are foundational to successful participation in society, and predict a suite of positive outcomes throughout life. It has long been asserted that free (i.e., unstructured) play is important for the development of self-regulation, but studies investigating play and self-regulation have faced empirical limitations. The current study used a large sample (n = 2213) from the Longitudinal Study of Australian Children to investigate time spent in unstructured quiet and active play activities at ages 2–3 and 4–5 years as a predictor of self-regulation abilities 2 years later. Children's play was reported by parents who completed a 24-hour time-use diary for 1 random weekend day and 1 weekday. Self-regulation was indexed at ages 4–5 and 6–7 by parent-, teacher- and observer-reported items comparable to similar large, longitudinal studies. Results showed that the more time children spent in unstructured quiet play Self-regulation skills are foundational to successful participation in society, and predict a suite of positive outcomes throughout life. It has long been asserted that free (i.e., unstructured) play is important for the development of self-regulation, but studies investigating play and self-regulation have faced empirical limitations. The current study used a large sample (n = 2213) from the Longitudinal Study of Australian Children to investigate time spent in unstructured quiet and active play in the toddler and preschool years, the better their self-regulation abilities at ages 4–5 and 6–7 years, even after controlling for earlier self-regulation abilities and other known predictors. Further, between 1 and 5 hours of preschoolers’ unstructured active play time significantly predicted self-regulation 2 years later. This study provides early support for parenting programs designed to increase opportunities for children to spend time in unstructured, free play in the early years.